WASHINGTON -- Sending a probe to the Kuiper Belt and its largest member, Pluto, should be NASA's first priority in solar system exploration, says a new report from the National Academies' National Research Council. Larger, more comprehensive efforts are also needed, beginning with a trip to Jupiter's moon Europa, said the committee that wrote the report.

"Solar system exploration is the grand human endeavor that seeks to discover the nature and origin of the system of planets in which we live, and find out whether life exists beyond Earth," said committee chair Michael Belton, president, Belton Space Exploration Initiatives, Tucson, Ariz. "To continue this exploration in the most productive way, using finite resources, NASA's missions must be prioritized."

The report outlines key objectives and associated missions that could be launched between 2003 and 2013. Objectives include learning how life developed in the solar system, determining whether life exists beyond Earth, understanding the nature and origin of the planets, and discovering how the laws of nature have led to the complexity of the solar system. To address these questions, NASA needs to send a series of robotic spacecraft ranging from small-scale undertakings that cost under $325 million to more extensive midsize missions that cost up to $650 million, the committee said. The small-scale missions should be launched at least once every 18 months.

The first of the midsize missions should be sent to the newly discovered and unexplored Kuiper Belt, which is a collection of primitive, icy objects beyond Neptune's orbit; some types of comets are thought to have originated there. Pluto, the largest member of the Kuiper Belt, is about 3 billion miles from Earth and is the only planet in the solar system that has not been directly observed by a robotic probe.

The administration's spending bill for NASA for fiscal year 2003, however, eliminates funding for a Pluto mission, citing the lack of community consensus on its importance. But the committee said a Kuiper Belt-Pluto mission should be a top priority because the science is compelling. Exploring the Kuiper Belt will contribute to a more complete understanding of planet formation and the origins of organic matter. Moreover, the technology exists today to build a probe that can visit and compare several objects and determine the diversity of their properties.

Larger missions should be deployed once every decade. These flagship missions, costing in excess of $650 million, will allow extended observation and experimentation, the report says. Priority for these missions should go to a spacecraft designed to explore Europa and confirm the presence or absence of an ocean under its icy surface. Europa is likely to contain the three things necessary for life to evolve -- liquid water, a source of heat, and organic material.

Other recommended midsize missions include collecting and returning to Earth samples from the Moon's South Pole, and deploying a Jupiter orbiter. Exploring a large impact basin located near the lunar South Pole will provide insight into the early history of the Earth-Moon system, added the committee. NASA also needs to create a new orbiter to carry probes to study Jupiter's atmosphere and determine if the planet has a core. To meet future exploration goals, the agency needs to make significant investments in new spacecraft and instrument technology, including the development of nuclear power sources and in-space nuclear propulsion. In addition, NASA needs to partner with the National Science Foundation to build and operate the Large-Aperture Synoptic Survey Telescope, a ground-based facility designed to search the sky and detect the majority of larger, near-Earth objects as well as observe more distant ones in the Kuiper Belt.

The study was sponsored by NASA. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows. The report New Frontiers in the Solar System: An Integrated Exploration Strategy is available on the Internet at http://www.nap.edu. Copies will be available for purchase later this summer from the National Academy Press; tel. (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).